The invention relates to a process for improving the adhesion of plastics to metals, particularly in the production of dental prostheses.
A process for applying a crown veneering to a metal prosthesis is known from German Offenlegungsschrift No. 32 11 123. The metal body is immersed once or several times in a silane solution and then dried. Onto the thus obtained silane layer is uniformly thinly applied a prosthesis plastic and subsequently the veneering shell produced according to known processes is pressed on, i.e. the prosthesis plastic is completely polymerized. Prior to silanization of the metal body, which is performed in an ultrasonic bath, the metal body is roughened by sandblasting. The disadvantage of this procedure is that it is only possible to use Si-containing base metal alloys and only ceramic veneering shells.
U.S. Pat. No. 4,364,731 discloses an adhesive layer of inorganic oxides, including silicon dioxide. This oxide layer is silanized and the veneering material is applied by known processes. The inorganic oxide layer is applied to the metal surface by using a sputtering apparatus. This process, requires an extremely accurate procedure for producing an undamaged jacket layer of inorganic oxides. Other processes proposed in this patent specification consist of coating from the vapor phase accompanied by chemical decomposition (CVD process) and plating using reactive ions.
German patent No. 34 03 894 relates to a modification of the procedure of the U.S. patent, which comprises applying the silicon dioxide layer with the aid of a flame hydrolysis burner using a gaseous, oxidizable silicon compound.
The aforementioned prior art processes are either only intended for specific material combinations used in dental prosthesis technology, or they require complicated and expensive apparatus not normally available in dental laboratories, and also an excellent controll of the process for obtaining an optimum adhesive layer. It is therefore necessary to precisely adhere to certain conditions, such as the spacing of the flame hydrolysis burner or sputtering apparatus with respect to the workpiece, e.g. the metal dental prosthesis.